1. Technical Field
The present invention relates to a timepiece dial, a method of manufacturing a timepiece dial, and a timepiece.
2. Related Art
Dials used in solar timepieces (timepieces that have a photovoltaic cell) must have the ability (light transparency) to pass enough light for the solar cell to produce enough electromotive force (emf) for timepiece operations. Plastic parts with excellent transparency have therefore generally been used for dials in solar timepieces. Compared with metals such as Au and Ag, however, plastic lacks a sense of luxury and an attractive appearance. A dial that is manufactured by bonding metal foil with a hole therein to a plastic substrate by means of an adhesive attempts to solve this problem as taught in Japanese Unexamined Patent Appl. Pub. JP-A-11-326549 (particularly from line 35, right column, page 3 to line 11, left column, page 4).
A problem with this method, however, is that the metal foil is easily wrinkled when the foil is applied to the substrate. Preventing such wrinkles requires extreme care in the bonding process, resulting in extremely low productivity in dial manufacture. Furthermore, even when extreme care is used in the bonding process, completely preventing the creation of relatively small wrinkles, for example, is difficult, and obtaining a sufficiently outstanding appearance in the finished dial is difficult. Another problem with this method is that a relatively high percentage of the dials are determined to be no good, which is undesirable in terms of both production yield and resource conservation.
These problems are particularly severe when the metal foil is relatively thin (such as 10 μm or less). Furthermore, when the metal foil is relatively thin (such as 10 μm or less), the foil tears easily during the adhesion process. This is undesirable with respect to dial productivity, production cost, and resource conservation. In addition, parts of the torn metal foil may be dispersed into the air, which is a concern for worker health.
There have also been attempts to coat the entire surface of a substrate with a metal film using a vapor phase formation method to form a coating so thin that light passes through, but such extremely thin metal films cannot produce a metallic luster with a sufficiently luxurious appearance, and cannot produce an appearance with the quality desired for a dial or timepiece.
Radio-controlled timepieces that receive radio signals and adjust the time accordingly have also quickly become common. Excellent transmittance of electromagnetic waves (radio waves) by the dial and other members is therefore also required in such radio-controlled timepieces. Solar-powered radio-controlled timepieces that have both an internal solar cell and an internal antenna for signal reception are also becoming common. As described above, a balance between an excellent decorative appearance and excellent transmittance of electromagnetic waves is therefore also needed in the dials used in such timepieces, but achieving both characteristics is extremely difficult.